Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern California Coastal & Inland Valleys
May, 2009
Regional Report

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Healthy roses stand a better chance to stave off pest infestations.

Rose Pests

I love roses. They are forgiving of my heavy-handed pruning, they provide cut flowers for the house, and they are very easy to grow, even for novice gardeners. Most roses will thrive on as much, or as little, care as you are willing to provide. By now you have enjoyed your first flush of blooms. The plants should be booming along nicely, but wait! Any moment you can expect a zillion aphids and their relatives to arrive for dinner.

Aphid Attack!
Aphids are soft-bodied insects that feed on plant juices. They will appear seemingly over night and infest tender, new growth on roses. Aphids may be green, brown, white, black, or pink and range in size from very tiny to the size of a pin head. Aphid pierce the soft tissue of new growth and then suck vital nutrients, which will eventually stunt the growth of the plant. Unfortunately, aphids can also transmit disease between plants, so you really do want to keep an eye out and control them before they become a problem. Look for infestations on soft, new growth at the tips of the branches.

Of all the insect pests, aphids are probably the easiest to control. Aphids are the preferred dining option for ladybugs, lacewing larvae, lizards, and some small birds. You never need to use pesticides, or even insecticidal soap to control aphids. Just use a blast of water from the hose to dislodge them. For some reason, they never find their way back to the plant. Be sure to do the water treatment early in the day so that the plants have time to dry before nightfall.

Which brings up another early season rose problem: fungal disease. Black spot is the most common, but rust and powdery mildew are right up there. Black spot is identified by circular black spots on the foliage. The spots may be outlined with a yellow border. Black spot can defoliate a plant, but that is an extreme case.

Powdery mildew looks like a furry powder coating on the leaves, stems, and flower buds. The best way to combat powdery mildew is to give your roses plenty of room so they get good air circulation. You can make a simple but effective fungicide by combining 2 teaspoons of baking soda with 1/2 teaspoon of horticultural oil and a drop of liquid soap mixed into one quart of warm water. Spray this on the plants at seven day intervals.

The best way to control fungal diseases, especially rust, is to keep the ground below the plants raked up and clean. Fungal spores are carried by water splashing onto the foliage, so by keeping the soil clean (is the term "clean soil" an oxymoron?) of fallen plant material that may be infested with disease spores, you will minimize the problem. Also, keep in mind that some varieties of roses are simply more susceptible to fungus problems than others.

Because roses are related to apples they are susceptible to fire blight. This bacterial disease will kill entire branches and eventually the whole plant. It starts at the tip of a branch, then desiccates the tissue as it moves down the stem, leaving the wood dry and black in color. Fire blight moves quickly, so early detection is mandatory! If the tip of a branch looks wilted even though the plant has ample water, chances are it is infected with fire blight. Cut the infected branches back to healthy wood, then sterilize your clippers with a 10 percent bleach solution. Fire blight is spread by ants, aphids, bees, houseflies, leafhoppers, and boring insects. It is also wind borne, so don't despair if one of your plants contracts the disease, it isn't your fault.

Rose beetles will chomp a few holes in the foliage -- hand pick when you see them. They are active early in the morning and again in the late afternoon.

Overall, roses are sturdy and won't give you much trouble. Keep in mind that a healthy plant has a better chance of surviving insect or fungus attack than a struggling one. Fast-draining soil, clean gardening habits, and regular garden inspections will keep your roses blooming through November!

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